The objective of this research is to investigate the relationship between various forms of hypertension in the rat and a mineralocorticoid (aldosterone) receptor located in smooth muscle cells and fibroblasts grown from the rat aorta. The receptor may be involved in the accumulation of water and electrolytes which occurs in the cells of the artery wall during the development of hypertension. This accumulation of water and electrolytes causes the cells to swell. This swelling narrows the lumen of the vessel, stiffens the vessel and increases the peripheral resistance. Initially, the capacity, specificity, and affinity of the receptor will be further characterized by Sephadex G 150 and ion exchange chromatography and temperature and a pH stability. For purposes of comparison, the glucocorticoid receptor, also present in these cells, will be characterized and quantitated. Both types of steroid aortic receptors in cells from strains of rats, which are resistant or susceptable to different types of hypertension, will be compared. The quantity of the aldosterone receptor will be compared to the fluid and electrolyte content of an aorta similar to that from which the cultured cells were derived. Elucidation of the relationship between hypertension in the rat and the aortic mineralocorticoid receptor may lead to an increased understanding of hypertension in both rat and man.